On uncoded high rate transmission over synchronous Gaussian multiple-access channels

On Gaussian multiple-access channels a penalty in power efficiency is to be paid if total transmission rate is higher than 1 bit/s/Hz per dimension. This usually results from the need for higher order modulation schemes required to maintain orthogonality of all users' signal waveforms. In this paper, we show that keeping binary modulation and accepting some multiple-access interference, is a more power efficient strategy by presenting simulation results of transmission systems outperforming orthogonal schemes for rates between 1.25 and 1.75 bit/s/Hz, per dimension.